Rear fog lamp. I'm not sure if it was required anywhere, but it was typically found on European Pagodas. Sometimes, I believe you'll see it installed below the rear bumper as well.
By the way, look how nicely that chrome trim fits underneath that EU rear license plate. It's a nice detail on European cars that we don't get here in the US. It visually "bridges" the rear bumpers really nicely. Then again, our plates aren't shaped the same so it doesn't really work as well visually.
Douglas Kim
New York, NY
280 SL #016220